The present, invention relates to a programmable automatic signal amplitude control circuit, and more particularly, to a programmable automatic signal amplitude control circuit applied in a high frequency related area.
In wireless communication system, a signal amplitude control circuit is required for adjust input signal variation. Conventionally, signal, amplitude is controlled by a closed loop signal amplitude control circuit.
A conventional signal amplitude control circuit is shown in FIG. 1, comprising a variable gain amplifier 1 with gain adjusted according to a control voltage applied from a negative feedback circuit 2 consisting of a peak detector 20 and a gain control circuit 21, the peak detector 20 detecting the amplitude of a signal output from the variable amplifier 1. The signal output from the peak detector 20 is then compared with a reference voltage Vref by a gain control circuit 21. Reference voltage Vref controls the value of the output signal Vc to maintain signal amplitude approaching a setup amplitude.
FIG. 2 illustrates a negative feedback circuit 2 based on a reference voltage Vref. A signal output from a peak detector is compared with a reference, voltage Vref through a transconductance unit 210 for outputting corresponding current signal. The current signal is converted to a corresponding control voltage signal Vc to control the variable gain amplifier 1 shown in FIG. 1.
FIG. 3 illustrates another negative feedback circuit 2′ according to a reference voltage Vref. An output signal from a peak detector 20 is compared with a reference voltage Vref through a comparator 211 and output as a comparison signal for controlling a switch SW. Current flows through capacitor C for integration to corresponding voltage, then converted to control voltage Vc through a gain control circuit or a level shifter 212.
As shown in FIG. 2, one terminal of the negative feedback circuit 2 receives the reference voltage Vref directly, while input signals at another terminal thereof are detected by the peak detector. Thus, input signals have more relative errors due to process variation during manufacture of the peak detector and Vref. As well, the conventional negative feedback circuit is based on reference voltage. To change output signal amplitude, multiple sets of reference voltage must be set, increasing circuit complexity.